Ventilatory patterns change during exercise in response to the increased oxygen demands of muscles and other tissues. Such changes are transient, and largely disappear once the metabolism slows down and any oxygen debt is repaid. Persisting with a regimen of moderate exercise, however, can cause more lasting physiological changes, including an increased capacity for oxygen metabolism in muscle groups exercised and an enhanced ability of the circulatory system to deliver oxygen to those muscle groups. Increased respiratory capacity of muscles from exercise is a direct response to increased rate of oxygen delivery to those muscles. During exercise the amount of oxygen taken up by the blood from the respiratory system must be distributed among various muscle groups according to their level of activity. Therefore the degree to which heavy activity can be focused to fewer muscle groups at a given maximum rate of oxygen uptake (VO2max), those muscles will experience a higher rate of oxygen delivery.
A number of applications can benefit from more effective and efficient modes of aerobic exercise. One is rehabilitative exercise for patients suffering the effects of congestive heart failure, vascular disease, and obstructive pulmonary disease. Often these patients have severely reduced exercise capacity and exhibit low VO2max values. Such low oxygen delivery cannot allow paired-limb exercise of sufficient intensity to provide an up-regulation of muscle aerobic capacity. This is particularly important to the prognosis of chronic heart failure patients, whose chances of surviving a heart transplant can be greatly increased by an increase in ventilatory threshold (an indicator of metabolic stress in skeletal muscle). Another application for which intensity of exercise is important is the training of endurance athletes. Exercise that produces greater gains in single leg ventilatory threshold would allow endurance athletes to perform for prolonged periods at close to VO2max without experiencing metabolic stress in skeletal muscle.
Applications such as these, point to a need for methods of exercise that isolate muscle groups such as those in a single limb. Also needed are devices that can facilitate such exercise. Many aerobic exercise methods are useful for concentrating a subject's exertions to certain muscle groups. Among the most effective methods for generating sustained aerobic activity are those that approximate locomotion. However such methods and the devices that implement them typically involve paired-limb activity. In this type of exercise the total oxygen uptake, less that required for other body processes, is more or less equally divided between two limbs. Therefore the maximum delivery rate experienced by each limb can only approach one-half of VO2max. To provide maximum gains in respiratory capacity, it has been recognized by the present inventors that it would be preferable to exercise each individual limb in isolation. In this way, each limb can receive oxygen at a rate much closer to VO2max, which can result in a greater adaptive response by the muscles of that limb.
Accordingly, the present invention provides a cardiovascular and muscle exercise device including a crank having an axis of rotation. A first arm can be connected to the crank and can be configured so that a downward external force applied to the distal end of the first arm causes rotation of the crank. The devices of the present invention can further include a second arm to which a counterweight is connected and configured such that the force applied by the counterweight causes rotation of the crank. In accordance with a more detailed aspect of the present invention, the device can include a brake. Another aspect of the invention includes a shield configured to prevent the counterweight from striking the subject during exercise.
In one embodiment of the invention the device can be a bicycle trainer or a retrofit bicycle trainer. In another aspect of the present invention a retrofit kit can be provided for modifying an existing device in order to accomplish the purposes of the present invention. The retrofit kit can include a counterweight and a fastener for attaching to the device.
The invention also provides a method of exercising musculature associated with a single limb, comprising the steps of applying a downward force to an arm operatively connected to a crank so that the arm moves from an upper position to a lower position. The crank can then be allowed to continue rotating so that the arm returns to the upper position. The return portion of the cycle is arranged such that the return movement is assisted by a counterweight.
Additional features and advantages of the invention will be apparent from the detailed description which follows, which illustrates, by way of example, features of the invention.